Damage or loss of the mechanoreceptors (hair cells) in the inner ear, are the leading cause for human deafness, because both are irreversible after birth. Unlike mammals, fish replace damaged hair cells throughout adulthood. This regenerative power is observed in the inner ear, but also in an evolutionary and physiologically related organ the lateral line. This superficial sensory organ offers a valuable tool to study in vivo the dynamic events of regeneration in time and in the context of a whole animal. Very few genes involved in regeneration have been identified so far, hampering progress towards restoring hair cells in humans. To address this particular point, the long-term objectives of this application are to elucidate the molecular events underlying the regeneration of hair cells in the lateral line. As an entry point, we are using a zebrafish mutant line (phoenix), which we have characterized. The mutated gene is novel and mutant larvae have a clear reduction in regenerated hair cells in the lateral line. The phoenix gene is expressed in supporting cells, which have been previously implicated as progenitor cells. They are not entering the cell cycle in the absence of phoenix. The first specific aim is to decipher the function of phoenix. To do so, we combine a cytological approach in fish cell lines with an expression screen in mutant larvae of previously known or newly discovered molecular players in the regeneration process. The second specific aim is to find partners of phoenix. We use genomic and a proteomic approaches in the wild type and phoenix mutant context. We are characterizing the transcriptome of each cell type of the lateral line and assess their changes during regeneration. The proteomic approach is based on co-immunoprecipitation in fish cells lines using an antibody against phoenix. In the third specific aim, we will pursue preliminary data showing that, phoenix localization is altered in human fibroblasts of Hutchinson-Gilford Progeria Syndrome patients, who are aging prematurely. Using immunoprecipitation coupled with mass spectroscopy, we will isolate and sequence the human homolog of phoenix. This work will provide insight into the genetics of regeneration of hair cells, opening up new therapeutic avenues.